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Topic: Arduino to control vehicle fans via pwm signal (Read 565 times) previous topic - next topic


I am trying to control the fan speed by sending a PWM to the fan modules. No signal and the fans go full high 5% and it should stay off. I had this working on a bread board but now that I moved it to a pref board I cannot control the fans anymore. This is how I have it wired currently any help would be appreciated.


This is probably a stupid question but did you connect the - side of your battery to the GND of the Arduino?

I hope this is helpful,



Resistors in the power rail?  Why?

Are the MOSFETs logic-level?
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Dec 04, 2017, 11:44 pm Last Edit: Dec 04, 2017, 11:56 pm by Boardburner2
Resistors in the power rail?  Why?

I suspect that diagram is somewhat incomplete , the j modules probably have their own supply.
Could still be an earth problem.

J291 and J671 appear to be automotive part nos.
On my car the fan is brushless.
Not at all sure they would be designed for PWM conntrol but do not know.


The fans are originally controlled by the engine control module via a pwm  signal to the fan modules for different speed. This is a engine swap and the new engine control module does not control fans.


I don't know if this helps but most (many) automotive PWM signals must work with a defined output vs PWM profile.

Typically 0 to 5% and 95% to 100% PWM is a failure mode, likely the 100% you mentioned.

The full range signal is likely;

5% PWM is off/low increasing to 95% is fast.  The 0 to 5% and 95 to 100% bands are not valid inputs.

Perhaps you need to go to something like 6 or 8% to turn it off.

Note each transition point (5% and 95%) has a +/- tolerance so in all likelihood 5% is not a defined operating area.


At this site;


The example connection was made on a BMW vehicle. This system varies the fan speed by a change in duty cycle of the signal. The fan is at rest at 10% and at maximum speed at 90%. The fan or fans have a constant-voltage supply with the earth return path being switched though the vehicle's electronic control unit (ECM).
It also show waveforms of the PWM.

Tom.. :)
Everything runs on smoke, let the smoke out, it stops running....


Dec 07, 2017, 12:53 pm Last Edit: Dec 07, 2017, 01:41 pm by Boardburner2
now that I moved it to a pref board I cannot control the fans anymore.

What exactly happens , cannot turn them off ?

When you moved from breadboard to perf did anything else change ? Running the engine  ?


What are the FET's you used ?
When you soldered the fets did you use an earthed workstation ?
It is possible they have failed, you should be able to test for this with a multimeter though.


Can you post some pictures of your assembled perf board, so we can see your component layout, please?

Do you have a DMM?

Thanks.. Tom.. :)
Everything runs on smoke, let the smoke out, it stops running....

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